The decision to strengthen the alliance's military presence in eastern Europe sends a clear signal to Moscow that NATO's security guarantees for Poland are real, Polish prime minister Donald Tusk said.

"This is a very powerful signal and our eastern neighbour cannot take this lightly," Mr Tusk said, in an apparent reference to Russia.

"The NATO security guarantees have ceased to be guarantees on paper and are starting to become actual guarantees."

Poland's president Bronislaw Komorowski said the rapid reaction force will likely amount to 5,000 soldiers.

World leaders have been discussing current global conflicts with particular interest paid to the crisis in Ukraine and the fight against Islamic State in the Middle East.

'Core coalition' to battle Islamic State

Mr Rasmussen said NATO will enhance cooperation on exchanging information on foreign fighters returning from the Middle East and help coordinate security assistance for Iraq with the possibility for assistance to include airlifts.

The United States said on Friday it was forming a "core coalition" to battle Islamic State militants in Iraq, calling for broad support from allies and partners but ruling out committing ground forces.

The defence and foreign ministers of the United States, Britain, France, Germany, Canada, Australia, Turkey, Italy, Poland and Denmark met on the sidelines of the NATO summit to discuss a strategy for addressing the Sunni militant group that has taken over swathes of Iraqi and Syrian territory.

"We need to attack them in ways that prevent them from taking over territory, to bolster the Iraqi security forces and others in the region who are prepared to take them on, without committing troops of our own," US secretary of state John Kerry told the meeting of 10 nations.

"Obviously I think that's a red line for everybody here - no boots on the ground."

Mr Kerry is calling for a plan to counter Islamic State in time for the United Nations General Assembly in September.

Cyber defence core task

The NATO leaders agreed on that a large-scale cyber attack on a member country could be considered an attack on the entire alliance, potentially triggering a military response.

The decision marks an expansion of the organisation's remit, reflecting new threats that can disable critical infrastructure, financial systems and the government without firing a shot.

"Today we declare that cyber defence is part of NATO's core task of collective defence," Mr Rasmussen said.

In 2007, a series of crippling cyber attacks paralysed much of NATO member Estonia in an apparent response to a dispute over the movement of a Soviet-era war memorial.

Most Western experts suspected the Kremlin was responsible but Russia denied it.

NATO reminds Russia: No third country has veto power

NATO, responding to Russian warnings against Ukraine's bid to join the western alliance, said on Friday that no third country could have a veto over its enlargement policy and took new steps to advance Georgia towards membership.

German chancellor Angela Merkel said NATO stands by a 1997 agreement on cooperation with Russia even though Moscow has breached it through its actions in Ukraine.

Ms Merkel told a news conference that leaders of the 28-nation alliance agreed at the summit that the NATO-Russia Founding Act remained a key part of Europe's security architecture.

Cooperation was suspended in March after Russia seized and annexed Crimea from Ukraine.

Ms Merkel said new European Union sanctions, due to be adopted on Friday over what she called Russia's illegal troop presence in eastern Ukraine, could be suspended if a promised ceasefire materialised and the crisis de-escalated.